Incremental Sheet Forming

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<ul><li><p>The technology of Incremental Sheet Forming A brief review of the history W.C. Emmensa*, G. Sebastianib, A.H. van den Boogaardc aCORUS RD&amp;T, PO Box 10.000, 1970 CA IJmuiden, The Netherlands bInstitute of Forming Technology and Lightweight Construction (IUL), Technische Universitt </p><p>Dortmund, Baroper Strasse 301, 44227 Dortmund, Germany cUniversity of Twente, PO Box 217, 7500 AE Enschede, The Netherlands *corresponding author: temporarily at the University of Twente, tel. +31 53 489 2675, fax: +31 </p><p>53 489 3471, e-mail address: w.c.emmens@utwente.nl Abstract This paper describes the history of Incremental Sheet Forming (ISF) focussing on technological </p><p>developments. These developments are in general protected by patents, so the paper can also be regarded as an overview of ISF patents in addition to a description of the early history. That history starts with the early work by Mason in 1978 and continues up to the present day. An extensive list of patents including Japanese patents is provided. </p><p>The overall conclusion is that ISF has received the attention of the world, in particular of the automotive industry, and that most proposed or suspected applications focus on the flexibility offered by the process. Only one patent has been found that is explicitly related to the enhancement of formability. Furthermore, most patents refer to TPIF (Two-Point Incremental Forming) as a process. </p><p>Besides simply presenting a historical overview the paper can act as an inspiration for the researcher, and present a rough idea of the patentability of new developments. </p><p> Keywords </p><p>Incremental sheet forming; SPIF; TPIF; AISF; patents; history </p><p>PACS code: 89.20 Bb 1. Introduction </p><p> 1.1 General introduction and scope. The last decade has shown an increasing interest in a new class of forming processes known as </p><p>Incremental Sheet forming (ISF). The name incremental forming is used for a variety of processes, all characterized by the fact that at any time only a small part of the product is actually being formed, and that the area of local deformation is moving over the entire product. This definition covers many processes, starting with the traditional blacksmith's hammering and its mechanical counterpart, the old forging hammer press. A variant is driving, a traditional technique still used for hand-making car bodies; this process has been automated to some extend. Also rolling can be regarded as an incremental process, although not always recognized or accepted as such. A particular incremental sheet metal forming process used at large scale is spinning, used for the manufacturing of rotational parts in low to medium large series like household cooking equipment. </p><p> This paper focuses on what is now generally known as Incremental Sheet Forming (ISF) or Asymmetric Incremental Sheet Forming (AISF), a definition of the process will be given in the next section. In 2005 an extensive review paper of ISF was published by Jeswiet et al. That paper described many aspects of this manufacturing process, but focussed on the more fundamental aspects and the 'make-ability' of products in the widest sense. Little attention however was given to specific technological developments. The present paper is not intended as an update of Jeswiet's </p></li><li><p>review, that would for example also have to include material and formability aspects. It is intended to highlight a special aspect by concentrating on the technological developments over the years from the earliest history, and by doing so it also presents a historical overview. The paper will do this by reviewing patents, for several reasons: </p><p> new developments are as a rule protected by patents, so patents provide a more or less complete overview; </p><p> patents are open publications, relatively easy to access; patents describe new features not presented before in other open publications; patents are often the only source of information about technological developments. The paper focuses on patents from the Western world, more precisely Europe and the USA. </p><p>Many patents have been issued outside that area, notably in Japan, A list of Japansese patents is provided as completely as possible, but these are not discussed in detail. Even within these limitations the paper does not claim to present a complete overview of all patents related to ISF, although it is considered to cover the major aspects. All patents discussed will be illustrated by a relevant figure from the patent description. Reference to patents in the text will be made by their unique number in square brackets, like [EP 12345678], a full reference list can be found in appendix 1 for American and European patents, and appendix 2 for Japanese patents. References to papers are made in the conventional way. </p><p>It should be noted that this list may include both issued patents as well as patent applications proposals. Since the patent law may differ significantly in each country, an issued patent may require a thorough proof of validity in the one country, where a simple declaration is sufficient in the other. As such, this overview of the given patents is not to be considered as a legal advice, but intended for the reader interested in history, for the researcher who might get new ideas, and for commercial applications to get a general (but possible incomplete) overview of which developments are covered (but not necessarily protected) by patents. The paper will pay some special attention to developments from the automotive industry. The reason for that is that history has shown that developments in, or demands from the automotive industry often lead to new developments in sheet metal working, and as such are important to follow. </p><p>This paper does refer to several older publications of which only a photocopy or scanned photocopy was available. Consequently the pictures taken from those publications are of poor quality. The graphs illustrating the patents are taken from pdf files, and hence are of limited resolution. </p><p>The scope as defined above also sets the structure of this paper. The history can be divided into three eras that are more based on the character of the developments than supplying a strict chronological division. Therefore the periods may overlap. </p><p> Period 1: -1996; this period can be regarded as the early history; although patents have been issued in that period that can be regarded as ISF (see next section), these did not lead to the present developments; these early developments used only SPIF (see next section for a definition); </p><p> Period 2: 1993-2000: this period showed many developments towards 'modern' ISF including other variants like TPIF (see next section), but exclusively in the Far East, and patents have been issued only in Japan; </p><p> Period 3: 2000-present: this patents showed increased activities in the Western World, and also the issue of patents there. </p><p>The paper will follow these three periods (sections 2, 3, and 4), period 1 will be examined by following the history from open publications. Section 5 will discus some patents that strictly speaking do not correspond to the ISF definition given below, but that are often studied as a parallel to ISF and are presented for reasons of completeness mainly. Section 6 finally presents a discussion on the (possible) application of ISF as concluded from the patents. </p><p> 1.2 Process definition </p></li><li><p>ISF and spinning are closely related. Both are incremental sheet forming processes with aspects in common, but there are some fundamental differences. As a general rule, in spinning a workpiece is clamped onto a rotating mandrel while the spinning tools approach the workpiece and deform it into the required shape. In conventional spinning the blank edge is moving inwards, and the material thickness is kept more or less constant. In shear spinning the blank edge is not moving inwards and the sheet thickness is reduced considerably. As in flow forming, the final wall thickness is determined by the distance between the tool and the mandrel. Basically, the mould determines the final shape. An excellent overview of the spinning process and its variations has been presented by Wong et al., 2003 </p><p>In most applications of ISF the blank edge is clamped and does not move inwards, although there are exceptions that will be mentioned below. The sheet is formed by having a tool follow the required shape in space, mostly by a succession of 'planar' contours or a single 'spiral' contour. The wall thickness reduces considerably but does not have to be controlled specifically. The absence of workpiece rotation allows an independent X and Y control allowing the manufacturing of asymmetric shapes, hence the name Asymmetric Incremental Sheet Forming (AISF), although its application obviously also includes symmetric shapes. The fundamental aspect is that the final shape is determined by the tool movement, not the mould (if any). Table 1 presents an overview of the basic aspects. </p><p>The blank edge is clamped for giving it a support mainly, as there is little tendency to pull the edge inwards. The blank may be left without any further support (Single Point Incremental Forming = SPIF), or there may be a simple support or a partial or full die (Two Point Incremental Forming = TPIF), the latter mainly for assisting in the creation of complex shapes. Also, the support may be replaced by a second small tool that is controlled independently from the first tool (Kinematic ISF). These variants are described in more detail below. In ISF the relative movement between tool and sheet is important, not which one moves and which one is held stationery. For the manufacturing of symmetric parts even the blank may rotate while still retaining the essentials of ISF. </p><p> Table 1. Comparison between spinning and ISF. spinning shear spinning ISF </p><p>blank edge moves inwards remains constant clamped wall thickness remains more or less </p><p>constant reduces, has to follow the sine lawb </p><p>reduces, determined by the processb </p><p>shape basically determined by </p><p>movement of roller, or by mandrel </p><p>mandrel movement of punch or roller </p><p>die/mandrel required yes (acts as fixture) yes no asymmetric shapes possible </p><p>limiteda no yes </p><p>a: although spinning is normally used for symmetrical products, asymmetric shapes can be made as well to some extent, see Awiszus and Meyer, 2005. </p><p>b: in shear spinning the final wall thickness has to be achieved by controlling the gap between roller and mandrel, in ISF the final wall thickness is determined by the characteristics of the process without need for direct control. </p><p> Consequently, for the purpose of this paper ISF is defined as: a family of sheet forming </p><p>processes where the deformation is highly localized, without drawing in of material from a surrounding area and using a fully clamped blank, where the final shape is determined by the xyz movement of some tool part without the need for a die. </p><p>Other definitions exist as well but discussion of those is beyond the scope of this paper. Many patents describe variants as well that strictly speaking do not follow this definition, for example by </p></li><li><p>allowing the blank edge to be pulled inwards for some reason. In the following these will be mentioned only briefly. </p><p> 2. First Period: early history (until 1996) This section describes the early developments before the first true ISF patent (1993). Also an </p><p>attempt is made to locate the origin of ISF. 2.1 Earliest history, until 1989 As stated above, the boundary between spinning and ISF is very thin. In the 20th century many </p><p>patents have been issued on variants of spinning that can be regarded as ISF process, or at least very close to that. Two of the most recent are mentioned here as examples, both from 1967, one issued to Leszak, and one to Berghahn of General Electric. </p><p>The Leszak patent [US 3342051, see appendix 1 for a full list of patents] describes a process for the manufacturing of disc-like or cup-like products from metal sheet. The blank rotates and vertical displacement is created by local bending that is caused by pushing the sheet into an elastic medium by a roller, see Fig. 1. The Berghahn patent [US 3316745] also describes a process for manufacturing disc-like products. Here a blank is clamped and rotates, while a roller moves inward along a radial line, thus describing a contour that forms the final shape, see Fig. 2. The patent refers to some older patents (the oldest from 1898!) describing related processes. </p><p>Fig.1. Process proposed by Leszak [US 3342051]. 6 = sheet, 7 = roller. </p><p>Fig.2. Process proposed by Berghahn [US 3316745]. 26 = roller, rolling on the sheet, </p><p> Both proposals have a distinct difference: in the Leszak proposal the shape is created by bending </p><p>of the sheet against an elastic medium, in the Berghahn proposal by the xyz movement of the roller. Some authors have mentioned the Leszak patent as being the origin of ISF, or at least an early example (Jeswiet et al, 2005). However if we follow our definition from section 1.2, then the Berghahn process can be regarded as ISF, and the Leszak process cannot. </p><p>Both patents are presented as variants of spinning. Although the Berghahn patent can be regarded as an example of ISF, it cannot be regarded as the origin of modern ISF, as there are no indications that this patent has indeed started the present developments. A proper way to find the origin of ISF is to back-track references. Papers on ISF often refer to older publications, and by tracking these one can follow the history backwards. This tracking ends with the work done by Mason (1978) of the Univ. of Nottingham, which in this respect can be regarded as the origin of ISF. </p><p>Mason has reviewed forming processes suitable for small batches. He then proposed a process </p></li><li><p>using a single spherical roller: "The minimum number of coordinates required to describe a shaped surface is three (x, y and z). A single spherical roller could follow this surface with three axes of control. A simple way to generate a shaped surface would be then to use a spherical roller working from one side". Noteworthy is that Mason assumes that a backing material is needed for all but the most simple shapes, and his work concentrates on finding a suitable backing material. He continues: "The shape could be produced by rolling the sphere backwards and forwards, and / or side to side across the surface of the sheet, while supported by some backing medium, increasing the depth of rolling by an increment at each pass .... To develop a shape this way point to point numerical control of the three axes x, y and z would be sufficient. It may be advantageous though to develop a shape progressively ... with the sphere following a curved path in one or even two planes, in which case a full three axes of continuous path numerical control will be desirable although not necessary." Some actual tests have been carried out, however in a more simple way by rotating the sheet clamped in a lathe, see figure 3. </p><p>Mason describes the very essenti...</p></li></ul>

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